Previous systems for the distribution of power in a limited distribution area with a source of limited power, such as in the case of an aircraft, generally include a master control unit to monitor and distribute alternating current (AC) power to seat mounted electronics boxes (SEBs), outlet units and associated cables. The components or line replaceable units (LRUs), mounting brackets, protective shrouds, extended cable runs etc. all contribute to the weight of conventional systems. U.S. Pat. No. 5,754,445, entitled “Load distribution and management system” and filed Dec. 20, 1995 discloses an exemplary distribution system. The disclosure of U.S. Pat. No. 5,754,445 is hereby incorporated by reference herein in its entirety.
Often, in passenger aircraft the master control unit (MCU) is mounted in an overhead area outside of the passenger space. The MCU distributes three-phase, high voltage power through a number of outputs to groups of SEBs located at the passenger seats. This power is then converted at each seat group to a form usable by the outlet unit (OU) assembly. This conversion is typically performed by a SEB. In the case of an AC system the power provided by the OU is typically 110 volts alternating current (VAC), 60 Hz. In the case of a DC or universal serial bus (USB) output, 28 volts direct current (VDC) is used to power USB outlets, which additionally convert the power locally to 5 VDC for powering USB devices.
In order to save cost and weight, it is desirable that the connected wires be as small as possible. However, if a connected wire were to become overloaded or experience a short circuit, it may be possible for the power source to provide enough current to overheat smaller connected wires. For this reason, wires in these “seat-to-seat” cables are sized to safely carry the maximum current available.
Seat mounted hardware, such as a SEB, requires a mounting bracket which often has a mass requirement designed to ensure the bracket holds the unit in place during a crash and also to protect from vibration and thermally transfer heat away from the SEB to maintain acceptable operating temperatures. In addition to the bracket and its mounting hardware, a shield in the form a metallic or plastic shroud covers the SEB to prevent inadvertent contact with the housing of the hardware. The bracket and shroud are often located on the seat leg or underneath the seat. In either case, the volume of these parts, along with the volume of the SEB, encroach on the passenger space.
In existing power delivery systems on aircraft, cable assemblies carry the power in a daisy chain fashion from one seat group to the next seat group. These cables typically connect to each other within the seat structures. The materials used in electrical wiring are limited in the maximum temperature they can tolerate without degradation. The operating temperature of a wire can be greatly affected by the size of the wire and the amount of current flowing in the wire can generate significant heat. For these reasons, the current in an electrical wire must be controlled to prevent degradation due to excessive heating. At the same amount of current, in comparison to a larger wire, a smaller wire has higher electrical resistance which generates more heat when the current flows through it. The cables connecting the seat groups are generally heavy gauge power wires with proper insulating properties to safely carry the maximum current available. Connector assemblies are often located low on the seat leg with a separate extension cable to where the SEB is located in the seat. Additional cables then route from the SEB to the outlet assembly(s).
All of the mentioned features add weight to the overall system in order to process original aircraft power to power that is suitable for use with passenger devices.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.